1. K+e+γ using OKA detector
Международная сессия-конференция Секции ядерной физики ОФН РАН «Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
A.Polyarush INR RAS
On behalf of «OKA» collaboration (IHEP-INR-JINR)
K+e+γ using OKA detector
The talk layout
OKA detector
Ke3 and Ke3γ decays selection
Background suppression
Results
Conclusions 1

2. Radiative K+e+γ decay
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г
Radiative K+e+γ decay
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3. Radiative K+e+γ decay
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
Radiative K+e+γ decay
The radiative K+e+γ decay allow as to perform quantitative tests CHPT, thanks to theoretical developments over the past couple of decades as well as recent and ongoing high-statistics experimental studies.
The first complete analysis within CHPT to O(p4) order was performed by Bijinens et al. [Nucl. Phys. B396 (1993) 81] Recently, the CHPT analysis was revisited and extended to O(p6) Kubis et al. [Eur Phys. J. C50 (2007) 557].
K+e+γ decay is one of kaon decays where new physics beyond Standard model can be probed. This decay is especially interesting as it is sensitive to T-odd contributions. According to CPT theorem, observation of T violation
is equivalent to observation of CP-violating effects.
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4. OKA: search for T-violation in K+ decays PDG 2016
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г
OKA: search for T-violation in K+ decays
PDG 2016
Br(K+e+γ ) = (2.56 ± 0.16)· A(ξ) = ± 0.024
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5. OKA detector
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1. Beam spectrometer:1mm pitch PC, ~1500 channels; Cherenkov counters
2. Decay volume with Veto system:
11m; Veto: 670 Lead-Scintillator sandwiches 20* (5mm Sc+1.5 mmPb), WLS readout
3. PC's and DT's for magnetic spectrometer:
~5000 ch. PC (2 mm pitch) DT (1 and 3 cm)
4. Pad(Matrix) Hodoscope ~300 ch. WLS+SiPM readout
5. Magnet: aperture 200*140 cm2
6. Gamma detectors: GAMS2000, EHS-backward EM cal. ~ 4000 LG.
7. Muon identification: GDA-100 HCAL+ 4 muon trigger counters behind
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6. Decay volume with Veto System
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
Decay volume with Veto System
Decay volume Veto System
Decay volume inside view
Veto System
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7. «Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
Statistics
OKA collaboration operate at IHEP PS U-70 in Protvino, Moscow region.
Detector is located in positive RF-separated beam with 12.5% of K-meson.
Nov 2010
Nov 2011
Nov 2012
Apr 2013
Dec 2015
Total
Beam, GeV/c
17.7
12.5
Live Kaons, 109
6.2
5.1
17.4
12.2
6.7
47.8
K2π, 106
15.2
15.5 61 42 16
~150
Ke3, 106
2.5
2.0
8.1 ~5
2.8
~20 7
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8. «Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
IHEP PS U-70
U-70 ring
IHEP Protvino
accelerator ring length 1.5 km
the size of the magnet as a truck
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9. Ke3 decay selection 2812875 Ke3 events with Eγ > 0.5GeV
1 ch. track 2mrad point to em-shower in ECAL: (r<4cm) <E/P<1.2
2 extra showers (ncl >3); <M<0.15 GeV
-angle between pK and pe 2mrad
2C -constrained fit χ2<20
Ke3 events
with Eγ > 0.5GeV
0.8 <E/P<1.2
0.11 <M<0.16 GeV
 - angle between pK and pe2mrad
M2mis = (pK - pe
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10. K+e+γ events selection
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
K+e+γ events selection
1) One positive charged track detected in tracking system and 4 showers
detected in electromagnetic calorimeters GAMS and EGS.
2) One shower must be associated with charged track.
3) Charged track is identified as positron.
4) Vertex situated within the decay volume.
5) The effective mass Mγγ for one γγ –pair is <M<0.15 GeV. .
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11. Background suppression
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
Background suppression
The main background channels for the decay K+e+γ are:
1) K+e+ with extra photon. The main source of extra photons are an interactions of electrons in the detector material.
2) K++ where one  photons not detected and + decays to e+ or misidentified as positron.
3) K++ with fake photon and + decayed or misidentified as positron. Fake photon clusters can come from + hadron interaction in the detector, external bremsstrahlung, accidentals. All these sources are included in our MC calculations.
4) K++γ when + decays or is miss-identified as an positron.
5) K+e+ when one γ is lost.
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12. Background suppression
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г.
Background suppression
Emiss > 0.5GeV, Eveto < 50 MэВ, <Zvx<-950, Eγ > 0.5GeV;
| Δy | = | y γ - y e+ | > 4 cm, Δy - vertical distance in GAMS plane;
|x,y| of reconstructed “ν” < 100cm in GAMS-2000 plane;
| M2miss (p0e+γ )|< GeV2;
MK > 0.45GeV;
4 mrad < θeγ < 40 mrad,
where M2miss (p0e+γ ) = (PK – Pπº – Pe – Pγ)2 ,
MK - K meson mass recovered, mass of the (e+γ)- system, assuming mν=0 .
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13. Experimental data K+ e+γ
cut 1
cut 2
1) Emiss > 0.5GeV and …
2) | Δy | = | y γ - y e+ | > 4 cm
3) |x,y| in GAMS-2000 of reconstructed “ν” < 100cm
4) |M2miss (π0e+γ )|< GeV2
5) MK > 0.45GeV
6) 4 mrad < θeγ < 40 mrad
cut 3
cut 4
cut 5
cut 6
M2miss(π0e+γ )
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14. Experimental data K+ e+γ
1) Emiss > 0.5GeV and …
2) | Δy | = | y γ - y e+ | > 4 cm
3) |x,y| in GAMS-2000 of reconstructed “ν” < 100cm
4) |M2miss (π0e+γ )|< GeV2
5) MK > 0.45GeV
6) 4 mrad < θeγ < 40 mrad MK
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15. MC signal Experimental data
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θeγ
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16. Background suppression
«Физика фундаментальных взаимодействий» 6-8 июня 2017 г
Background suppression
Cut
Real data
Ke3
Kπ3
Kπ2
Signal
Emiss > 0.5GeV, Z, veto
515612
395930
19869
7138
62670
Δy > 4 cm
65093
10396
13975
1373
29190
|x,y| “ν” < 100cm
44363
7385
8726
1027
21950
MK > 0.045GeV
23446
3801
2901
333
17030
|M2 miss (e+γ )|< GeV2
20739
3520
398
298
16120
4 mrad < θeγ < 40 mrad
13118
1239
225
138
12040
Table 1
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17. «Физика фундаментальных взаимодействий» 6-8 июня 2017 г
Results
Experiment
Bg + signal
Background
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18. «Физика фундаментальных взаимодействий» 6-8 июня 2017 г
Results
After applying cuts 1 to 6, we received 13,118 candidates.
For E*γ > 10MeV and 0.6 <cos*θ <0.9 we have 3435 selected events with background events. Comparing this after efficiency correction with ours Ke3 events, for the relative branching ratio we got
R=Г(K+e+γ ) / Г(K+e+) = (0.59 ± 0.02 ±0.03) ·10-2
Systematic errors are estimated by variation of cuts of Table 1 and using two different ways of backgrounds normalization.
Theoretical prediction for R from CHPT is R = 0.56 ·10-2
For T-odd asymmetry we got:
Aξ = 𝟏𝟔𝟐𝟐−𝟏𝟓𝟔𝟏 𝟑𝟏𝟖𝟑 =− 0.019± ± 0.030
Theoretical prediction in Standard Model is Aξ = −0.59·10 −4 .
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19. «Физика фундаментальных взаимодействий» 6-8 июня 2017 г
Results
Nev
R exp · 10 -2
Reference
3435
0.59 ± 0.02 ± 0.03
This work
1456
0.48 ± 0.02 ± 0.03
ISTRA+ 82
0.46 ± 0.08
XEBC
192
0.56 ± 0.04
ISTRA 13
0.76 ± 0.28
HLBC
Table 20
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20. «Физика фундаментальных взаимодействий» 6-8 июня 2017 г
Summary
1) collaboration, operating at IHEP Protvino U-70 PS in RF-separated beam,
has accumulated large statistics of K+ decays.
2) K+e+γ decay signal is extracted with a low background.
3) R = Г(K+e+γ ) / Г(K+e+) = (0.59 ± 0.02 ±0.03) ·10-2
for the region E*γ > 10 MeV and 0.6 <cos*θ eγ <0.9 at statistic 3435 events.
4) Asymmetry in the T-odd variable ξ A(ξ) = ± 0.020± 0.03
for the region E*γ > 10 MeV and 0.6 <cos*θ eγ <0.9
Next step – to measure SD terms.
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